1. Field of the Invention
The present invention relates to a map data transmitting technology that enables transmission of map data to be used at an information terminal such as a navigation apparatus mounted in a vehicle through communication.
2. Description of the Related Art
There is an information communication-based navigation system in the related art that mainly comprises a navigation apparatus installed in a vehicle and an information transmitting center that executes a route search to determine a route to a destination or transmits map data in response to a request issued from the navigation apparatus. In the existing map data transmitting method adopted in the information communication-based navigation system, map data obtained by slicing data within a specific range around the route are transmitted in the original form. However, background data contained in the map data may include polygon data indicating a background with a planar area such as an ocean, a lake or a field. A given set of polygon data indicates a specific contour with an area boundary line defined by a plurality of nodes connected with one another. Thus, if a portion of such polygon data is contained in the specific range and nodes corresponding to this range alone are extracted, the connection of the area boundary line becomes cut off and, as a result, the correct shape of the planar area cannot be represented. This point is not addressed in the related art.